As a magnetic recording medium, there has been a magnetic tape cassette having a pair of tape reels, around which a magnetic tape is wound and which is rotatably contained in a cassette case. FIG. 10 is an exploded perspective view of a magnetic tape cassette for a DVC (a digital video cassette) as one example of the magnetic tape cassettes of this type.
As shown in FIG. 10, a cassette case of this magnetic tape cassette 50 is composed of an upper cassette half (hereinafter referred to as an upper half) 51 in a substantially rectangular shape, and a lower cassette half (hereinafter referred to as a lower half) 52. The lower half 52 is formed, at its center part, with two reel holding holes 53a, 53b, and at its front face with a space 54 for inserting a tape withdrawing member which is provided on a recording and reproducing apparatus.
Also, at the front face of the lower half 52, there is formed a lower half portion 55a of a front wall 55 which defines this space 54, and at both sides of the space 54, there are respectively formed cut-outs 57a, 57b for introducing a magnetic tape 56 to the exterior and to the interior. There are further provided tape guides 58a, 58b respectively between ends of the lower half portion 55a of the front wall 55 and the cut-outs 57a, 57b. On the other hand, the upper half 51 is also provided, at its front face, with an upper half portion 55b of the front wall 55 which defines the space 54 for inserting the tape withdrawing member which is provided on the recording and reproducing device.
To the cassette case composed of the above described upper and lower halves 51, 52, is assembled an openable lid 60 so as to cover the magnetic tape 56 which is stretched across the above described space 54, in other words, exposed to the exterior from the cassette case, on such occasion as this cassette case is carried. This openable lid 60 is composed of three lids, namely, an outer lid (a front lid) 61, a top lid (an upper lid) 62, and an inner lid (a rear lid) 63.
Tape reels 70, 80 around which the magnetic tape 56 is wound are contained in the above described cassette case so as to rotate in a state where they are respectively inserted in the above described reel holding holes 53a, 53b. These tape reels 70, 80 are composed of upper flanges 71, 81 and lower flanges 72, 82 restricting vertical movements of the magnetic tape 56, and bosses 73, 83 which are integrally formed with the lower flanges 72, 82 and around which the magnetic tape 56 is wound.
FIG. 11 is an enlarged view of an area surrounding the tape guide 58a. As shown in FIG. 11, the tape guide 58a which is formed between the end of the lower half 55a of the front wall 55 and the cut-out 57a guides the magnetic tape 56. This magnetic tape 56 is wound around the bosses 73, 83 of the magnetic tape reels 70, 80 as described above. When the openable lid 60 is closed, that is, when the magnetic tape 56 is not running for play back or so, positioning of the magnetic tape 56 in a vertical direction is conducted by means of the lower flanges 72, 82 and ribs 59a, 59b which are formed at the front end of the above described lower half 52.
By the way, there exist several magnetic tape cassettes having the above described structure, whose cassette cases are the same in height (size in a vertical direction) and different in size in a horizontal direction. More specifically, in such magnetic tape cassettes, diameters of the tape reels are made different in order to vary winding amounts of the magnetic tapes (duration of recording time), and the tape reels are respectively contained in the cassette cases which are different in size only in a horizontal direction. In order to deal with the magnetic tape cassettes which are different in size in this manner, there are disclosed for example, in registered Japanese Patents Nos. 2636825, 2636826 and so on, such recording and reproducing apparatuses which are capable of operating a plurality of the magnetic tape cassettes in the same manner.
Conventionally, as the magnetic tape cassettes to be loaded in such a recording and reproducing apparatus, there have been a large cassette having a relatively long recording time (hereinafter referred to simply as “an L cassette”), a small cassette having a relatively short recording time (hereinafter referred to simply as “an S cassette”), and a cassette having a medium recording time (hereinafter referred to simply as “an M cassette”). However, they are not so different in size. Therefore, even though a thickness of the cassette case of the L cassette is the same as a thickness of the cassette case of the S cassette, there has been no problem in the L cassette with respect to strength.
In recent years, there has been an increasing need for using a further larger cassette than the above described L cassette (hereinafter referred to simply as “an LL cassette”) for the purpose of further increasing the recording time. However, provided that a height of the LL cassette should be maintained to be the same as the height of the above described S and L cassettes while a thickness of the LL cassette is maintained to be equal to the thickness of the other cassettes, there will be arisen such a problem that a flexure may occur in the cassette case, in other words, a problem of strength, because the LL cassette has a larger area in a horizontal direction. For this reason, it is necessary to take such a countermeasure for the LL cassette that the thickness of the cassette case is increased. In this case, if it is intended to ensure an increased amount in size of the thickness of the cassette case by varying the height of the LL cassette, the recording and reproducing apparatus must be inevitably upsized correspondingly, and a problem of an increased cost may be concerned. From this viewpoint, it has been considered that the vertical size of the LL cassette had better be maintained at the same size as it currently stands.
However, when the strength of the cassette case is intended to be ensured by increasing the thickness of the LL cassette without changing the vertical size of the LL cassette, gaps inside the LL cassette will become narrow. On the other hand, because the tape reels are such members as rotating inside the cassette case when driven, the gaps of a certain extent must be maintained between the cassette case and the tape reels so that the rotation may not be hindered.
Therefore, in order to obtain the predetermined gaps between the cassette case and the tape reels, such a method has been considered that a distance between the upper and the lower flanges composing the tape reels may be reduced to such an extent that a lateral size of the magnetic tape may not be interfered, in other words, the lower flanges may be positioned at a higher level and the upper flanges may be positioned at a lower level than in the S cassette and the L cassette. However, as described above, positioning of the magnetic tape cassette in the vertical direction is conducted by means of the lower flanges and the ribs provided at the front end of the lower half. For this reason, by taking this countermeasure, a difference in height between portions where the magnetic tape starts to be wound (radially inner portions of the lower flanges) and tape withdrawing portions (the aforesaid ribs of the lower half) will be too large in the LL cassette. As a result, the tape may be, so to say, slackened when the openable lid is closed, and there has been such probability that edges of the tape may be damaged.
FIG. 12 is a plan view of the lower half 52 of the DVC, in which (a) shows the lower half 52 of the DVC of the M cassette and (b) shows that of the L cassette. A distance between the positioning holes 90a, 90b for positioning them when loaded in the recording and reproducing apparatus, as well as a distance between a pair of the tape guides 58a, 58b provided in forward parts of the cassette are the same both in the M cassette and the L cassette. This is because a recording and reproducing head, tape guide pins, and so on can be co-used with both the cassettes in the recording and reproducing apparatus.
Here in the drawings, hatched areas are tape running areas S in the recording and reproducing apparatus. The L cassette is larger than the M cassette in an outer shape, while distances between the tape guides 58a and 58b are equal in both the cassettes. Bosses 91a, 91b for small screws cooperate with the tape guides 58a, 58b to define tape running openings 92. A width of the tape running opening 92 in the L cassette is larger than that of the tape running opening 92 in the M cassette.
Accordingly, the tape running areas S of the L cassette are larger in width than the tape running areas S of the M cassette in the recording and reproducing apparatus. For this reason, no additional member can be provided in areas corresponding to the tape running areas S of the L cassette in the recording and reproducing apparatus, and so, an effective use of an interior of the recording and reproducing apparatus is impossible.
Moreover, in case where it has become necessary to mount an additional member near the opening of the cassette in the recording and reproducing apparatus, the member must be mounted avoiding the tape running areas S of the L cassette. This will incur upsizing of the recording and reproducing apparatus.
Further, the magnetic tape cassettes are classified into those for personal use and those for business use according to their applications. FIG. 13 is an exploded perspective view showing main components of a beta cam L cassette which is a magnetic tape cassette for business use.
As shown in FIG. 13, this beta cam L cassette 220 is substantially composed of an upper half 224 and a lower half 222 constituting a cassette case, a pair of pay-off and take-up tape reels 228, 230 which are rotatably contained in the upper and lower halves 224, 222 and have a magnetic tape 226 wound around, and a lid 232 for covering front openings of the upper and lower halves 224, 222 so as to be opened and closed.
In addition to the above, there are provided a plurality of small screws 234 for joining the upper and lower halves 224, 222 with each other, a pair of guide rollers 236 and a pair of guide pins 238 made of metal which are arranged at tape pay-off and take-up openings in the lower half 222, and so on. Further, in the drawing, reference numeral 246 represents reel holders arranged on the tape reels 228, 230, reference numeral 248 represents reel springs for biasing the tape reels 228, 230 via the reel holders 246, and reference numeral 250 represents center caps for locking the reel springs 248 from above the upper half 224.
Pads 244 press the magnetic tape 228 with appropriate biasing force by slidably contacting their side faces with a back face of a magnetic tape 228 which passes between the guide rollers 236 and the guide pins 238 at the opening end. A magnetic tape 226 taken out from the cassette 220 is guided by means of a variety of guide pins, which are not shown, in the recording and reproducing apparatus, wound around a head which is not shown, and then, paid off or taken up according to rotation of a capstan motor.
Among the above described various components, the guide rollers 236 are formed of resin molded articles such as POM, for example, which has smoothness and mechanical strength. Moreover, each of the guide rollers 236 is formed in a barrel-like shape in its exterior, as shown in FIG. 14, for the purpose of ensuring safe running of the magnetic tape 226 and guiding it effectively, and supported so as to rotate by idly engaging its center hole 236a with a bearing pin which is projected from the lower half 224.
Generally, on occasion of injection molding of such a molded article, a parting line PL between molds is positioned on an end face of the molded article as shown in FIG. 14. As a result, when it is molded into a barrel-like shape, a larger diameter portion swelling at the middle is made undercut, and the article cannot be extracted in case where it has a larger swelling amount than a certain value. Therefore, it has been usually formed into the barrel-like shape through a cutting work by machine from a rod-like material.
However, in case where the cutting work by machine has been employed, there has been such a problem that cutting amount has been large at both the ends, requiring a lot of working time. In addition, because the work requires an expensive machine such as an NC lathe, a cutting cost would be extraordinary high.